This invention relates generally to improvements in butterfly valve plates, particularly of the type used in relatively high mass flow and high pressure pneumatic flow control applications. More specifically, this invention relates to an improved butterfly type valve plate for use in a pneumatic surge valve or the like, wherein the valve plate is designed for reduced noise with increased mass flow capacity.
Butterfly type valve plates are utilized in a variety of pneumatic flow control applications for regulating the flow of a gas such as air along a flow conduit. In general terms, the valve plate comprises a disk of generally circular shape which is mounted on a pivot stem or shaft along the flow conduit for movement between a closed position oriented generally perpendicular to a central axis of the flow conduit, and a full open position extending generally parallel to the flow conduit axis. A system controller is often provided for response to selected system parameters such as pressure or the like to modulate the position of the valve plate between the open and closed positions.
Butterfly type valve plates are commonly used in pneumatic surge valves employed in an auxiliary power unit or system for operating the environmental control system of an aircraft on the ground. Such auxiliary power units comprise a gas turbine engine which drives a compressor to supply compressed air to the aircraft. The actual demand for compressed air may vary in accordance with system load, such that excess air may be provided at varying intervals by the auxiliary power unit. A surge valve responding typically to selected system pressures modulates the position of a butterfly valve plate mounted along a bypass flow conduit through which excess air is relieved to the exhaust side of the gas turbine engine. Such surge valves must be designed with a relatively high mass flow capacity, yet meet increasingly stringent noise limitations.
In the past, valve plates for use in high pressure surge valves have been the subject of considerable design effort to reduce noise by stabilizing flow particularly at the downstream side of the butterfly shaped valve plate. Such designs are typified, for example, by the valve plate structures and related noise suppression devices disclosed in U.S. Pat. Nos. 3,238,955; 3,960,177; and 3,677,297.
A continuing need has existed, however, for further improvements in surge valve design for achieving noise reduction, particularly in a valve plate design which does not decrease but preferably increases mass flow capacity through the surge valve. The present invention provides an improved butterfly valve plate construction which fulfills these needs and provides further related advantages.